The April 2010 Deepwater Horizon disaster led to the largest ever marine oil spill. Individuals were exposed to a range of toxicants and stressors that could lead to adverse effects. The GuLF Long-term Follow-up Study (GuLF STUDY) was designed to investigate relationships between oil spill exposures and a wide range of potential physical and mental health effects among workers involved in response and cleanup following this disaster. This piece of the study focuses on developing and refining methods to assess chemical exposure.